1. Field of the Invention
The present invention relates to a transmitting and receiving system for digital network communication on electric power-lines by means of using transmitting- and receiving devices, of which each includes a piezoelectric substrate and two coded interdigital transducers (IDTs).
2. Description of the Prior Art
Electric power-lines are greatly desired to be used for digital network communication. If a code division multiple access (CDMA) method avails for digital communication on electric power-lines, it is possible to make a transmission speed, in spread spectrum communication, high. In addition, if a surface acoustic wave (SAW) matched filter is incorporated in the CDMA method, it is possible to make the transmission speed still higher. However, it is difficult for a conventional type of CDMA method with the SAW matched filter to realize a base-band communication because of a coded message-signal under the condition of a phase shift keying (PSK) burst-signal. In other words, it is necessary to transduce the PSK burst-signal to a digital pulse signal with a high speed for the base-band communication. In order to make the digital pulse signal, the use of a complicated circuit is unavoidable for the conventional type of CDMA method with the SAW matched filter.
An object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines comprising transmitting- and receiving devices.
Another object of the present invention is to provide the transmitting device capable of coding a message digital-signal applied thereto, and delivering the message digital-signal as a coded digital-signal into electric power-lines.
Another object of the present invention is to provide the receiving device capable of receiving the coded digital-signal from the electric power-lines, and detecting an output digital-signal corresponding to the message digital-signal.
Another object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines capable of making the coded digital-signal, in the digital network, play a role as a pseudo-noise to keep a base-band communication secret.
Another object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines capable of recognizing each other in the digital network.
Another object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines capable of low electric power consumption.
Another object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines excellent in durability and manufacturing.
A still other object of the present invention is to provide a transmitting and receiving system for digital communication on electric power-lines having a small size which is very light in weight and has a simple structure.
According to one aspect of the present invention there is provided a transmitting and receiving system for digital communication on electric power-lines comprising a transmitting device and a receiving device. The transmitting device consists of an input terminal, a bipolar-pulse generator, a first piezoelectric substrate, a first coded IDT, a second coded IDT, a first intermediary IDT, an electrode group, a synchronizing device, an envelope detecting device, a monopolar-pulse generator, and a mixer connected with electric power-lines. The electrode group consists of two sideward IDTs and a central IDT between the sideward IDTs. The synchronizing device is connected between the first intermediary IDT and one of the sideward IDTs. The envelope detecting device is connected with the central IDT. The receiving device consists of a receiving connector connected with the electric power-lines, a tuning coil, a second piezoelectric substrate, a second intermediary IDT, a third coded IDT, a fourth coded IDT, a detecting device, and a detecting terminal. The first-, second-, third-, and fourth coded IDTs, consisting of at least three interdigital electrode pairs, respectively, have first-, second-, third-, and fourth coded patterns, respectively.
If monopolar pulses of a message digital-signal are applied to the bipolar-pulse generator via the input terminal, the monopolar pulses are transduced to high-frequency bipolar-pulses (xe2x88x921 and 1). When the high-frequency bipolar pulses (xe2x88x921 and 1) are applied to the first- and second coded IDTs, respectively, first- and second surface acoustic waves (SAWs) corresponding to the first- and second coded patterns, respectively, are excited on the first piezoelectric substrate. The first- and second SAWs are detected at the first intermediary IDT as first- and second coded burst-signals, respectively. When the first coded burst-signal arrives at the sideward IDTs simultaneously, third- and fourth SAWs are excited on the first piezoelectric substrate 3. The third SAW takes a form of burst signal with the same phase state via the synchronizing device. The third- and fourth SAWs arrive at the central IDT simultaneously. And then, a first coded digital-signal is obtained at the monopolar-pulse generator via the envelope detecting device. In the same way, a second coded digital-signal is obtained at the monopolar-pulse generator. Thus, the first- and second coded digital-signals are delivered into the electric power-lines via the mixer.
On the other hand, if the first coded digital-signal is received at the receiving connector, the first coded digital-signal is applied to the second intermediary IDT via the tuning coil. In this time, a fifth SAW is excited on the second piezoelectric substrate. When the fifth SAW corresponds to the third coded pattern, a first decoded pulse is detected at the third coded IDT. In the same way, a second decoded pulse is detected at the fourth coded IDT. Thus, an output digital-signal, which is composed of the first- and second decoded pulses and is equivalent to the message digital-signal, is detected at the detecting terminal via the detecting device.
According to another aspect of the present invention there is provided a bipolar-pulse generator in place of the monopolar-pulse generator. The use of the bipolar-pulse generator enables a high-frequency transmission excellent in transmitting ability on the electric power-lines.
According to another aspect of the present invention there are provided first-, second-, third-, and fourth coded IDTs, having first-, second-, third-, and fourth coded patterns, respectively, which are changed in accordance with a designated time region, respectively.
According to another aspect of the present invention there is provided a transmitting device that the propagation direction of the first- and second SAWs is orthogonal to that of the third- and fourth SAWs.
According to another aspect of the present invention there is provided first- and second piezoelectric substrates, made of a piezoelectric ceramic plate, respectively, the polarization axis thereof being parallel to the thickness direction thereof.
According to another aspect of the present invention there is provided a subdevice, which is located between the tuning coil and the second intermediary IDT and consists of a third piezoelectric substrate, an input IDT, an output IDT located in parallel with the input IDT, an envelope detecting device, and a bipolar-pulse generator.
In the subdevice incorporated into the receiving device, when the first coded digital-signal is applied to the input IDT via the tuning coil, a SAW is excited on the third piezoelectric substrate. The SAW is detected at the output IDT as a first coded row of bursts. And then, a first coded row of digital-pulses is caused at the envelope detecting device. The first coded row of digital-pulses is transduced to a first coded row of high-frequency bipolar-pulses at the bipolar-pulse generator. Thus, the first coded row of high-frequency bipolar-pulses is applied to the second intermediary IDT. In the same way, a second coded row of high-frequency bipolar-pulses is applied to the second intermediary IDT.
According to other aspect of the present invention there are provided transmitting and receiving devices. The transmitting device consists of an input terminal, a first bipolar-pulse generator, a first piezoelectric substrate, first- and second coded IDTs, a first electrode-group, an envelope detecting device connected with the first electrode-group, a monopolar-pulse generator, and a mixer connected with electric power-lines. The receiving device consists of a receiving connector connected with the electric power-lines, a tuning coil, a second piezoelectric substrate, a second electrode-group, a second bipolar-pulse generator, an intermediary IDT, third- and fourth coded IDTs, a detecting device, and a detecting terminal. The first-, second-, third-, and fourth coded IDTs consist of at least three interdigital electrode pairs Pi (i=1, 2, . . . , n), respectively, of which two neighbors are at a distance L from each other. The first-, second-, third-, and fourth coded IDTs have first-, second-, third-, and fourth coded patterns, respectively. The third- and fourth coded patterns are in reverse to the first- and second coded patterns, respectively. The first electrode-group consists of an interdigital electrode A0 and an interdigital electrode Ai (i=1) at a distance iL (i=1) from the interdigital electrode A0. The second electrode-group consists of a central interdigital electrode B0, a left interdigital electrode Bxe2x88x921 at a distance L0 from the central interdigital electrode B0, and an interdigital electrode Bi (i=1) at a distance L0+iL (i=1) from the central interdigital electrode B0.
When the high-frequency bipolar pulses (xe2x88x921 and 1) are applied to the first- and second coded IDTs, respectively, first- and second SAWs are excited on the first piezoelectric substrate, respectively. The first SAW is detected as a first coded burst-signal at interdigital electrode A0, and after a time corresponding to the distance L, at interdigital electrode A1 again. As a result, the monopolar-pulse generator causes, via the envelope detecting device, a first double-coded digital-signal. In the same way, a second double-coded digital-signal is generated at the monopolar-pulse generator. Thus, the first- and second double-coded digital-signals are delivered into the electric power-lines via the mixer.
On the other hand, if the first double-coded digital-signal is applied to the left interdigital electrode Bxe2x88x921 and right interdigital electrode B1 via the tuning coil, third- and fourth SAWs are excited on the second piezoelectric substrate. The third SAW arrives at the central interdigital electrode B0 by a time corresponding to the distance L before the fourth SAW arrives at central interdigital electrode B0. As a result, the first double-coded digital-signal is transduced to a first monocoded burst-signal at central interdigital electrode B0. The first monocoded burst-signal is transduced to a first monocoded digital-signal at the bipolar-pulse generator. When the first monocoded digital-signal is applied to the second intermediary IDT, a fifth SAW is excited on the second piezoelectric substrate When the fifth SAW corresponds to the third coded pattern, a first decoded pulse is detected at the third coded IDT. In the same way, a second decoded pulse is detected at the fourth coded IDT. As a result, an output digital-signal, which is composed of the first- and second decoded pulses and is equivalent to the message digital-signal, is detected at the detecting terminal via the detecting device. The use of the first- and second electrode-groups enable a double-coding and double-decoding system.
According to a further aspect of the present invention there are provided first- and second electrode-groups. The first electrode-group includes at least two interdigital electrodes Ai {i=1, 2, . . . , (nxe2x88x921)} at a distance iL {i=1, 2, . . . , (nxe2x88x921)}, respectively, from the interdigital electrode A0. The second electrode-group includes at least two right interdigital electrodes Bi {i=1, 2, . . . , (nxe2x88x921)} at a distance L0+iL {i=1, 2, . . . , (nxe2x88x921)}, respectively, from the central interdigital electrode B0. When the interdigital electrodes Ai take turns in connecting with the envelope detecting device, the interdigital electrodes Bi take turns in connecting with the receiving connector. The use of the first- and second electrode-groups enable a complicated double-coding and double-decoding system.